1. Field of the Invention
This invention involves a sequential process for the preferential extraction of vanadium and uranium from wet process acids employing neutral organo-phosphorus compounds and dialkylphosphoric acids.
2. Brief Description of the Prior Art
Phosphoric acid generally is produced commercially by one of two methods. One method generally is called the "furnace" method, and the other generally is referred to as the "wet process" method. In the wet process method of producing phosphoric acid, phosphate rock is contacted with a mineral acid such as sulfuric acid. Most phosphate rock contains metal compounds in varying amounts. In many cases, these metal compounds are dissolved from the phosphate rock and appear in the wet process acid as contaminants. Vanadium and uranium compounds are among those dissolved from the phosphate rock, particularly when the rock is from the so-called western deposits of Idaho, Wyoming, Utah and Montana.
Vanadium, however, is an undesirable component of wet process phosphoric acid in that it prevents the use of the phosphoric acid in making animal feed supplements, as the amount of vanadium must be kept at a low level in such animal feed supplements. Similarly, uranium is undesirable in such feed supplements.
On the other hand, vanadium and uranium are valuable materials and wet process phosphoric acid can be an important source of these materials. Therefore, a process for the sequential recovery of vanadium and uranium from wet process phosphoric acid provides an important benefit, in that the vanadium and uranium are converted from undesirable contaminants to valuable by-products.
There have been many attempts made in the past to recover vanadium from wet process acid. One such process is described in U.S. Pat. No. 2,211,119 wherein the vanadium is extracted from the acid with an organic extractant which preferably comprises isopropyl ether. U.S. Pat. No. 3,131,993 describes a process in which the preferred organic extractant is di(2 ethylhexyl)phosphoric acid. In U.S. Pat. No. 3,700,415, assigned to the same assignee as the present invention, there is described a process for extracting vanadium from wet process phosphoric acid utilizing certain neutral organophosphorus compounds as an extractant. U.S. Pat. No. 3,734,696, assigned to the same assignee as the present invention, discloses a process for extracting vanadium from acidic mixtures containing fluoride using aliphatic amines as an extractant.
Further, there have been several processes developed for recovering uranium from wet process acids derived from eastern phosphate deposits. Typical of such uranium recovery processes is U.S. Pat. No. 2,859,092, using alkylphosphoric, alkylphosphonic and alkylphosphitic acids as an extractant and U.S. Pat. Nos. 2,859,094 and 3,711,591 using, as an extractant, a mixture of a dialkyl phosphoric acid and a neutral organophosphorus compound.
Furthermore, in U.S. Pat. No. 3,826,476, assigned to the same assignee as the present invention, there is described a process for the simultaneous coextraction of uranium and vanadium from wet process phosphoric acid utilizing, as an extractant, a mixture of dialkyl phosphoric acid, trialkylphosphine oxide and an organic diluent.